Lawn mowers of the general type involved in this invention have been available for many years. They employ a housing on which is mounted a gasoline or electric motor. The motor provides power through a rotating shaft to a blade which rotates within the housing in a plane generally parallel to the ground. Grass that is cut is forced both by mechanical impingement and by centrifugal force vertically upward or radially outward to a discharge port in the housing.
Lawn mowers of the prior art have consistently had several problems. Grass cuttings tend to fall back through the blade and avoid collection. Moist cuttings accumulate and clog the housing. Grass cuttings clog the discharge port thereby aggravating these problems.
The prior art has attempted to provide solutions to these problems by designing cutting systems which employ specially constructed housings and associated blades. Typical attempts are shown in U.S. Pat. Nos. 3,192,692; 3,601,960 and 4,158,279 which describe a variety of housing shapes and blade configurations.
U.S. Pat. No. 3,192,692, which issued to Slemmons, shows a semi-toroidal housing situated above the blade to provide a space to collect and discharge grass clippings through a discharge port located in the upper portion of the housing. A very specific blade construction is required to provide efficient collection and discharge of the grass.
U.S. Pat. No. 3,601,960, which issued to Buechler, describes a volute-shaped housing having a side discharge chute. A disc-shaped lower lip defines the access opening to the blades. A passage is provided radially outward from the tip of the blade. This passage increases in size as the volute expands in radius towards the discharge chute. Again a blade is constructed with unique features to enhance the collection and discharge characteristics of the housing.
U.S. Pat. No. 4,158,279, which issued to Jackson, describes a cylindrical housing having a radial extending lower lip similar to Buechler. An enlarged area is provided over the plane of the blades to collect the clippings as in Slemmons. Here, as in the earlier patents, a special blade configuration is used which requires the bolting of enlarged impellers to the tips of the blades opposite to the cutting edge to mechanically increase the upward movement of the grass clippings.
The functioning of the cutting systems of the prior art is mainly dependent on the centrifugal forces of the radially flowing air created within the housing by the rotating blade.
In the Buechler patent several steps are taken to enhance the centrifugal flow. The first is the construction of gutters in the upper blade surface to maintain the grass clippings on this upper surface where they will be directed radially outward. Additionally, vents are provided in the upper housing which, in association with impellers, create secondary airstreams to suppress the grass clippings towards the blade. The overall result in combination with the extended lower wall and lip is to provide an enhancement of the centrifugal effect to improve the efficiency of discharge through the volute-shaped side discharge port.
Since the art has moved from the side discharge system of the Buechler patent to the rearward discharge similar to the Slemmons patent and the Jackson patent, centrifugal force is insufficient to provide efficient collection and discharge. An upward motion now must be imparted to the grass clippings in order to discharge from above the blade instead of radially outward at the tip of the blade. This problem was attacked in general by the use of blade shapes which provide, through mechanical impingement, an upward motion to the grass clippings as in the Slemmons and Jackson patents. The use of special blade designs increases the complexity and expense of the blade.
It is the object of this invention to provide greatly improved collection efficiency while utilizing a standard blade common in the industry.
It is also the object of this invention to enhance the beneficial effects of the centrifugal airflow through the use of a unique housing design which is simple to manufacture.
It is another object of this invention to minimize the blade requirements and avoid the need for complex shapes or the need for close tolerances between the blade and housing.